1. Field of the Invention
The present invention relates to an image pickup apparatus which synthesizes a plurality of image frames produced by continuously taking images of a subject to produce a synthesized image.
2. Description of Related Art
A conventional image pickup apparatus such as a digital camera forms an optical image of a subject by means of an optical lens, and converts the optical image into an electric signal by means of an image pickup device such as a CMOS image sensor.
As a method for taking images in a dark place, there is known a method in which images of a subject are continuously taken with exposure time having smaller hand jiggle, the images are added while correcting motion of the plurality of images, thereby producing one image.
In the case of the patent document 1, however, a predetermined number of images are collectively continuously taken previously and then, the images are synthesized into one image. Therefore, if a long time is required to obtain the last image after the start of the image-taking processing, it takes lots of time to take photograph again when a user recognizes the image-taking processing has failed.
Further, since the number of images to be synthesized is predetermined, when images are taken in an extremely dark place, there is a problem that even if the predetermined pieces of images are synthesized, the image does not become sufficiently bright.
When an image of a person is taken in a dark place against a night piece backdrop, a difference in brightness between a face of the person and a bright portion of the night piece is large. Therefore, there is a problem that in order to sufficiently brighten the face of the person to sufficiently provide gradation, the number of images to be synthesized must be sufficiently high so that the synthesized image is sufficiently bright.
The sufficient and necessary number of continuously taken images is varied depending upon an image-taking condition of a subject. It seems possible to always take images more than necessary to avoid the shortage of the number of images to be synthesized, but there is a problem that a user must hold the camera for a long time without jiggling his or her hand.